Ring Final Circuits (OK I don`t think that Flameport likes them!)

[ebee]

Well (just for clarity - I was brought up in the "Rings are Kings Era" so I could be a little biased) . Rings V Radials both have advantages and disadvantages so it`s a horses for courses kind of thing to me.
Some (a large part of the world) avoid rings and do not see a need for them, in fact if they had only been invented today I think that they would probably almost universally be voted down as a daft idea. On the other extreme some think you can not truly be an electrician if you don`t do and understand the ring final circuit. Personally I think both extremes are wrong.
PS even advocates' of rings usually have always done lighting circuits as radials - I know of only one electrician who did lighting circuits as a ring type configuration.

(I usually have done earthing of lighting circuits a bit "ringlike" - ie two or more lighting circuits in an installation, I would find a way to link both circuits earths part way down the circuit because of the possible benefit) of A/ redundancy in case of a break in the earth connection and B/ To some degrees lowers R2 which is good rather than bad.
The easiest way to achieve this is to have somewhere a 2 gang switch and the switches connected to different circuits, say example upstairs/downstairs lighting circuits. Taking care to disconnect the "other cpc of a lighting circuit" do all the tests including R2 then do the opposite way round.
That way you would note the R2 of each lighting circuit and then with both circuits earths connected repeat the R2 tests at all places and note the differences. Every little helps?

 

[ericmark]

It is nice reading post #31 to see some one using their brain rather than either the regulations say, or we have always done it this way. Full marks to @ebee

I have seen some ring finals which did not follow the normal design, one was in a fridge, OK the fridge was the size of 3 houses, but they wanted to be able to use cleaning machinery inside the fridge, i.e. vacuum cleaner etc. So wanted an array of 13 amp sockets to plug these machines into.

There was around a 3 to 4 meter drop from the ceiling to the position of the sockets, and one could walk on the ceiling, so a 6 mm² SWA was run around the ceiling into boxes above each 13 amp socket position, and a spur dropped from each box to the socket below it. This method reduced volt drop, and kept the loop impedance low enough, unlikely more that 3 items used at any one time, so whole lot on a 32 amp overload.

Be it a redundant cooker supply feeding a ring final rather than take two separate cables back to the CU or a figure of 8 arrangement some times one needs to only only think out of the box to install them, but also test them, using the R1 R2 method is not going to work with a fig of 8, only way to ensure the loop impedance is within limits is to test at the socket.

We are not plumbers, we need to use the knowledge we have and design a system to do the job, not simply say this it the way we have always done it.

 

[securespark]

I don't like ring finals and agree that 4 milli stranded is easier to work than 2.5 solid.

I also think it's better having (for example) two radials than one big ring.

You do minimise inconvenience if something goes wrong. Yes, I know some of you have said it's a once in a blue moon scenario, but then many of us would agree insurance cover for a breakdown for example would save a load of hassle. You may not need it but when you do, it will save you inconvenience and potentially money too.

 

[securespark]

What I mean is that the regulation 433.1.204 is still written for a BS7671 30A fuse and its CCC derating requirements.

Did you mean 3036?

I'm not being picky (), it's just for clarity).

 

[EFLImpudence]

Well (just for clarity - I was brought up in the "Rings are Kings Era" so I could be a little biased) . Rings V Radials both have advantages and disadvantages so it`s a horses for courses kind of thing to me.

Quite possibly but for new installations we no longer use BS3036 fuses so the argument does not apply.

Some (a large part of the world) avoid rings and do not see a need for them,

There is no need for them nowadays.

in fact if they had only been invented today I think that they would probably almost universally be voted down as a daft idea.

They would NOT BE invented nowadays because the reasons for them no longer exist.

On the other extreme some think you can not truly be an electrician if you don`t do and understand the ring final circuit. Personally I think both extremes are wrong.
PS even advocates' of rings usually have always done lighting circuits as radials - I know of only one electrician who did lighting circuits as a ring type configuration.

(I usually have done earthing of lighting circuits a bit "ringlike" - ie two or more lighting circuits in an installation, I would find a way to link both circuits earths part way down the circuit because of the possible benefit) of A/ redundancy in case of a break in the earth connection and B/ To some degrees lowers R2 which is good rather than bad.
The easiest way to achieve this is to have somewhere a 2 gang switch and the switches connected to different circuits, say example upstairs/downstairs lighting circuits. Taking care to disconnect the "other cpc of a lighting circuit" do all the tests including R2 then do the opposite way round.
That way you would note the R2 of each lighting circuit and then with both circuits earths connected repeat the R2 tests at all places and note the differences. Every little helps?

None of that is the same as the UK ring final with conductors rated lower than the OPD.

 

[EFLImpudence]

Did you mean 3036?

I'm not being picky (), it's just for clarity).

Yes, of course, thanks, I will alter it.

 

[SUNRAY]

(I usually have done earthing of lighting circuits a bit "ringlike" - ie two or more lighting circuits in an installation, I would find a way to link both circuits earths part way down the circuit because of the possible benefit) of A/ redundancy in case of a break in the earth connection and B/ To some degrees lowers R2 which is good rather than bad.
The easiest way to achieve this is to have somewhere a 2 gang switch and the switches connected to different circuits, say example upstairs/downstairs lighting circuits. Taking care to disconnect the "other cpc of a lighting circuit" do all the tests including R2 then do the opposite way round.
That way you would note the R2 of each lighting circuit and then with both circuits earths connected repeat the R2 tests at all places and note the differences. Every little helps?

With respect I think we'd all expect to see all earth conductors at a switch connected together regardless of which OCPD circuit they originate from and additionally if tests are being performed at that point I can't think of many who would deliberately disconnect earths to perform them. The same is also true to a lesser extent in other situations such as the use of these:

Where 2 different circuits, such as power RFC and a lighting socket, are brought together in the enclosure.

Let's also not forget the RFC is connected to the boiler and hence the water pipes which are also connected to the electric shower circuit and the immersion heater.

All of a sudden we find the earths of every circuit in a small property are connected together in addition to any main gas and water arrangements at the CU.

 

[EFLImpudence]

Another point:

I would say the UK ring final today is similar to the cooker circuit with a 32A MCB yet 6mm² cable.

The reason for the 6mm² cable - as with the ring, originally required because of the 30A BS3036 fuse - has disappeared but people still do it as a matter of habit because people still do it as a matter of habit.

Of course, there might occasionally be a legitimate reason for 6mm² cable but generally there is no need - like the ring.

 

[ebee]

old habits etc. 6.0 and a 30a cooker circuit, then some showers were ok at 6.0 and the 4.0 was not a well used size so with many the 1.0 or 1..5 then 2.5 then 6.0 covered most jobs so 4.0 was not very popular and the price comparison reflected that

 

[EFLImpudence]

old habits etc.

Exactly. That's what I said.

No electrical reasons today to maintain those habits.

 

[blup]

One advantage of a ring final is that it produces two radials if things go wrong.

Blup

 

[EFLImpudence]

That is actually a disadvantage.

2.5mm² conductor and 32A MCB - even worse if still 30A fuse.

 

[SUNRAY]

Hmmm let's design a circuit, a 32A sockets radial requiring 100m of cable in a domestic property.

What I see is the amazing advantage of not requiring a few metres of cable back to the CU.

What I also see is the impossible task of getting two 16mm² cables into every accessory.

Apologies if the current maximum length of a 2.5mm² ring final is no longer 106m.

As I've previously mentioned I don't have a particular allegiance to either version of a RFC.

 

[EFLImpudence]

Don't be silly.

 

[SUNRAY]

Don't be silly.

Who's being silly?